The invention relates to a bearing for the printing head of a matrix printer, of the type having a number of slidable printing pins which are journalled in the printing head and whose printing ends are situated in the vicinity of each other on a straight line which extends transversely of the direction of a line to be printed. A bearing which can be inserted into the printing head guides the pins near their printing ends. Such a bearing typically provides an individual, substantially straight guide channel for each printing pin, and includes a portion which is made of comparatively soft material and a portion which is made of comparatively hard material.
The invention furthermore relates to a printing head comprising such a bearing.
Very severe requirements are imposed on the mechanical parts of the printing head of comtemporary matrix printers, both the printing pins themselves and the bearings of the printing pins, particularly those operating at high printing speeds. The bearings of the printing pins should have a high wear resistance as well as a construction of low weight. Particularly the so-called nose bearing of the printing pins which is situated near the printing spot should have as low as possible a weight in view of the high speed at which the printing head is displaced along a record carrier. Therefore, the nose bearing of a printing head is preferably made partly of a synthetic material of the kind described, for example, in U.S. Pat. No. 3,991,870.
Bearings of the described kind are often used in printing heads of matrix printers in which the guide channels or movement paths of the printing pins have a curved shape. In printers of this kind the printing pins converge towards the printing spot. The converging printing pins are customarily guided over a comparatively short distance, near the printing spot, in straight guide channels provided in the nose bearing. The free ends of the printing pins which are intended for printing are situated on a vertical, straight line which extends transversely of the direction of a line to be printed. The movement paths of the outer printing pins (viewed in the nose bearing) are curved more than the movement paths of the printing pins situated nearer to the center, so that the walls of the outer guide channels are subject to more frictional wear than the walls of the other guide channels.
In order to reduce the wear of parts of the nose bearing, bearings of this kind in U.S. Pat. Nos. 3,991,870, 3,991,871 and 4,009,772 utilize inserts of a material which is substantially harder than the material used for the remainder of the nose bearing. The insert thus forms part of the nose bearing which can be replaced as a unit. The guide channels of the printing are formed in the very hard material of the inserts.
These known printing heads have the cast disadvantage that the provision of guide channels in the insert is an elaborate and hence comparatively expensive operation.